The present invention relates to a system for removing material such as solids from a pressurized vessel without relieving the vessel pressure.
In a typical application, such as any pressurized coal gasification process, the ash and slag from the process are dropped into a water bath at the bottom of the reactor vessel. The problem presented is to remove this residue of ash and slag without relieving the pressure in the vessel.
The removal of solids from pressurized vessels is generally accomplished by either one of two systems, referred to as a blow out system and a lock hopper system. The blow out system consists of a choke through which the solids are forced by means of the pressure differential between the vessel interior and exterior. Control of solids flow is effected by varying the choke throat diameter. Some of the drawbacks of this system are the enormous amounts of make-up water required, the inefficient use of energy required for throttling in order to control the flow, and the energy required merely to pressurize the large amount of make-up water needed. The lock hopper system consists of a lock between the vessel interior and exterior through which the solids are passed for removal from the vessel. Enormous energy is expended by this system every time the lock cycles since the transfer of the solids can only be accomplished between areas having equal pressures. In addition to a large energy requirement, the system works as a batch process, which produces a non-linear flow of solids. The resulting temporary back up of solids between lock cycles may create problems within the vessel. Large quantities of make-up water are also required by this system, creating an energy usage that is similar to that found in the blow out system.
In accordance with the present invention, a linear pocket letdown device has been designed to provide for the removal of material from the vessel in such a way as not to relieve the vessel pressure.
An object of the present invention is to provide a substantially more efficient means than any now employed to remove material from pressurized processes.